Brown is a warm color within the auric spectrum. It corresponds to the element of earth and to the Root Chakra and Solar Plexus (since many browns tend to be in the orange and red families).
Keywords to describe a brown aura person would be: physical, giving, sociable, grounded, friendly, natural, practical, brave, fragile, logical.
A more in-depth analysis of what a brown aura means can be found in my previous entry here. Many shades of this color are listed, so you can find your specific shade meaning easily. :)